Method of making corrugated fibre board and products obtained thereby



1966 A. GOLDSTEIN ETAL 3,29 05 METHOD OF MAKING CORRUGATED FIBRE BOARDAND PRODUCTS OBTAINED THEREBY Filed April 18, 1962 4 Sheets-Sheet 1 INVENTORS 1413 9 91941! Gocos 1-5119 BY M09174 4 04. F

Dec. 6, 1966 A. GOLDSTEIN ETAL 3,290,205

METHOD OF MAKING CORRUGATED FIBRE BOARD AND PRODUCTS OBTAINED THEREBYFiled April 18, 1962 4 Sheets-Sheet 2 INVENTORS 4694/94? GOL067'E h NMA/ A/ou 6 47'7'o4wE/s Dec. 6, 1966 A. GOLDSTEIN ETAL 3,290,205

METHOD OF MAKING CORRUGATED FIBRE BOARD AND PRODUCTS OBTAINED THEREBYFiled April 18, 1962 4 Sheets-Sheet 4 E 3 5 I I l kl/9'7 -olseaadwcnuwrnoo v a) O O (6 e0 Q o N 6) O. O

3, I O i r '1] u U 9, Q \l |f a 4 l l l l 3 3 3 g 9 g 1NvENToRs r AB AMMGowsrsw "-2! J0 'W/ZOW/ ya/unkind BY M0, 4y WOLF Z A N575 United StatesPatent l 3,290,205 METHOD OF MAKING CORRUGATED FIBRE BOARD AND PRODUCTSOBTAINED THEREBY Abraham Goldstein, Plainview, and Murray Wolf, KewGardens, N.Y., assignors to Tri-Wall Containers, Inc., New York, N.Y., acorporation of New York Filed Apr. 18, 1962, Ser. No. 188,508 Claims.(Cl. 161-137) This invention essentially relates to a method of makingmultiple wall corrugated fibre (or paper) board of the thick and verythick kind comprising at least two and preferably three layers or pliesof corrugated mediums and three of four liners and to the productsobtained thereby. The corrugated mediums are thus interposed orsandwiched between, these spaced liners which are flat sheets adhesivelysecured to the tips of the corrugated medium to form an integratedproduct.

Particularly the triple wall product has the advantage over other fibreboard materials when made into boxes, of having great column strengthand therefore permitting a number of the boxes to be piled one on top ofanother when containing heavy objects, without causing excessivebuckling or complete collapse of the vertical walls of the boxes nearthe bottom. Another advantage is that this product has great resistanceagainst the tearing penetration occasioned by sharp objects strikingagainst it, such as might occur when boxes are transported and subjectedto careless treatment.

The great column strength is obtained because the liners or flat sheetsare spread very widely apart away from the neutral axis and the tearresistance is obtained because of the multiple layers of material.However, these properties are obtained to a high degree only after thetips of the corrugations of the corrugated medium are adhesively securedfirmly to the liners or flat sheets throughout the construction of theproduct.

In order to manufacture the product one flat liner sheet is adhesivelybonded to one web of corrugated medium by adhesive or glue applied tothe tips or crests of the corrugations or flutes across the entire widthof the latter which are parallel to each other, so as to form a layerknown as a single face corrugated board. This is done twice or threetimes according as a double wall or a triple wall corrugated board iscontemplated. Then the single face boards are preheated to condition thesheets for the reception of adhesive and the exposed ridges of thecorrugations on the unlined side of the corrugated medium of each of thetwo or three layers have adhesive applied to them across their entireWidth and the two or three layers are superimposed and pressed togetherwith a third or fourth outermost liner whereby said ridges of saidcorrugation are .adhesively secured to the liner of an adjacent ply andto said outer third or fourth liner. While pressure is continuouslyapplied to the composite board thus obtained, the latter is heated topartially dry it for bonding the several sheets together whereby thesheets are incompletely set. For triple wall corrugated board thisheating may be effected preferably at a tempera- 3 90,205 Patented Dec.6, 1966 ture within the range of approximately 300 to 350 F. Thecomposite board is then cooled to allow handling thereof and possiblysubsequently scored or creased transversely to the corrugations topermit folding or bending the material to a packaging shape and possiblycrushed locally and trimmed and cut to finished size. All of saidoperations may be effected manually but they are generally moreconveniently carried out while the material is continuously moving withthe corrugations transverse to the path of travel in a single passthrough an automatic corrugated fibre board machine comprising two orthree corrugating and single facer sections followed by a combiningdouble backer device incorporating a laminating, heating and coolingsection and a scoring and shearing section. The temperature-speedrelationship is varied with the humidity, the thickness, and porosity ofthe sheets to provide a residence time in the heating section to set orharden said adhesive. Thus for example the web of triple wall corrugatedboard may be heated for not less than 14 seconds and not more than 24seconds (otherwise the product is scorched).

The medium which is relatively cheap may have any furnish and may evenbe glassine paper. However, in the manufacture of shipping containersthis sheet is generally composed of paper made by the kraft pulpingprocess, paper made by the semi-chemical pulping process, paper madefrom waste papers or paper made from the pulping of straw. The linerwhich is relatively expensive can again have any furnish but isgenerally a sheet of all kraft furnish or a sheet with waste paperfurnish.

The purpose of the adhesive is to adhere the mediums to the liners.rugated board operate at relatively high speed, the adhesive must bondor at least set immediately. When an adhesive is set, it has undergoneeither a physical or chemical change to an extent such that thematerials between which it lies are sufficiently adhered so that theycannot be separated easily. Further physical or chemical changes onlyserve to help develop maximum bond strength in the adhesive. This latterperiod is a curing or a bonding period.

It is an object of the present invention to provide an improved methodof making multiple Wall corrugated fibre board having increased rigidityand strength and preferably pertaining to the triple wall type. Thismethod is remarkable notably in that among other operations known per seit comprises the step of tensioning said liners end to end by stretchingsame to positively maintain their flatness throughout the manufacturingprocess, the step of assembling the component layers in their freshlymade and slightly damp state with all of the adhesive incompletely setby simultaneously and continuously pressing them firmly together whilethe liners are held taut and the component parts are prevented from anyslippage relative to each other, the moisture but not all of it thenbeing progressively driven off substantially uniformly by heating, thestep of cooling the resulting composite board while still tensioned andimmediately thereafter possibly scoring said board as required byfolding, while some moisture still remains therein, and possibly thestep of stacking the finished product cut to size for a curing time toallow the remaining moisture to evaporate i and the board components toeventually acquire a stabi- Since the machines used to produce cor--lized moisture content with respect to the humidity of the surroundingatmosphere.

It is surprising that when the triple wall product is made as describedwith an overall weight practically the same as that of the prior artdouble and triple wall products, the former exhibits so much greaterstrength this prevailing whether it is manually made or made in acorrugated paper board machine. Concerning the time and temperaturevalues, both of these vary over wide limits. The great strength of thenew triple wall product thus obtained is for instance due to maintainingthe liners tensioned to keep them absolutely flat during the wholeprocess without any relative slippage between any of the parts such asmight smear the glue freshly applied or rupture the glue of thepreviously glued parts. Furthermore, if the finished product is to 'bescored to permit the folding of flaps and the like, this should be doneimmediately after the cooling stop because at that time the productstill retains some of its moisture and although its glue is set, it isstill slightly flexible, thereby facilitating the crushing which formsthe score lines or strips without substantial harm to any of the layersor to the glue connections. The result is a product that is structurallybalanced and firmly interconnected.

Instead of using the relatively heavy weight paper liners used to makesingle wall and double wall prior art products, the triple wall productresulting from the above procedure is tremendously stronger in every waythan is the double wall product even though the weight of the liners ofboth is substantially the same. In other words, the triple wall productmay be made with relatively thinner or lighter weight paper liners.

The adhesives used comprise essentially starch and water which must beheated to a high enough temperature to cause the starch to gel, or asilicate type adhesive such as sodium silicate and water which must beheated to evaporate the water to set the adhesive. Thus heat isrequire-d in both instances.

It is not very difficult to get heat to the adhesive at the time thesingle layer of corrugated medium is applied to the single layer ofliner or flat sheet. However, serious problems occur when attempting toget the proper amount of heat to the adhesive after the various layershave been combined to form the three layers of corrugated medium andfour layers of liner or flat sheet materials.

Such problems are increased if the liner is made thicker to provide thefinished product with greater column strength and tear resistance, or ifthe corrugated medium is shaped with large or high corrugations tospread liners farther apart as is indicated to increase the columnstrength by placing the liners farther from the neutral axis.Preferably, both outermost liners are of greater weight than the innerliners to attain the greatest possible moment of inertia. Thicker linerssoak up more water when the adhesive is applied and their very thicknessreduces their ability to conduct heat. Higher corrugations contain moreair which reduces the flow of heat and in addition spaces the liners andadhesive farther from the heat which can only be applied to one side ofthe combined pieces when any convenient manufacturing method is used.

If excessive heat is applied to one side of the combined layers to tryto get enough heat to the far side, then there is the possibility ofover-heating the adhesive close to the source of heat. Both kinds ofadhesive when over-heated become brittle and tend to break away fromtheir desired locations and from the normally desired form or shape ofthe adhesive material as it is located between the parts it must holdtogether. -Now it can be appreciated that normal ways for attempting tomake this triple wallcorrugated fibre board with greater strength, areself defeating.

According to the present invention, the production of multiple wallcorrugated fibre board especially of the triple wall type whose minimumstrength is better than similar known board made with the same overallweight of liners or flat sheets incorporated in only three flat sheetsor liners and only two webs of corrugated medium between them and whosemaximum strength is considerably greater than this is made possible in apractical way. This is done by making the outermost liners or fiatsheets of paper not only of greater weight but according to anotherfeature of the invention also by employing liners of very great densityobtained by using highly calendered paper.

In addition, according to a further feature of this invention themanufacturing of the separate single face layers comprises the step ofgluing the ridges of the flutes of the corrugated medium which are to beadhered to the liner with an adhesive compounded to set at relativelyhigh temperatures; thus when securing the single layers of liner anadhesive is used, whether of the starch or silicate kind, which requiresa large amount of heat to set it properly and which therefore can laterwithstand satisfactorily higher temperatures. The use of this kind ofadhesive is practical because at this time there is no great problem ingetting heat to the adhesive.

Then at the. later time according to still another feature of theinvention, when the several for example three single face layers ofcorrugated medium and liner are juxtaposed or brought together with anextra for example fourth outermost liner required to produce the finalproduct, an adhesive is used, and again it may be either of the starchor silicate type, which is compounded to set at lower temperatures.

The advantages are that although the liner is of heavy weight and greatstrength, being highly calendered, its high density and relativethinness permits the heat to pass through it more readily. Furthermore,when the final combining step is carried out a large amount of heat canbe passed through the product to set the adhesive requiring the lowertemperature to set this adhesive satisfactorily without hurting thepreviously applied adhesive having the higher temperature settingcharacteristic.

A well-established principle of mechanical engineering is that thegreatest strength and rigidity in a structural member having a givenamount of material is realized by disposing the surfaces subjected tostress so that they are as far apart as possible to provide the greatestmoment of inertia. Therefore it is known to spread the liners or fiatsheets as far apart as possible, and in the case of triple wall boardfor example to use corrugated mediums two of which are made withcorrugations that are quite high while the third is made with acorrugation of lesser height. Then according to a further feature of theinvention, the parts are combined so that the corrugations of lesserheight are closest to the heat source used to set the adhesive requiredto inter-connect the various layers of the final product. Therefore, theheat does not have to travel a great distance before reaching the firstzone of adhesive used in the second or overall combining step. At thesame time all of the layers are spread rather widely apart from theneutral axis of the material of the product. Furthermore, cartons madefrom the board described are easier to fabricate and use.

As a further and preferred elaboration of the invention, the adhesivesapplied during the combining step also differ from each other incharacteristics. Those applied to the corrugation tips closest to theheat source may be compounded to set at somewhat higher temperaturesthan the adhesive used to affix the latter furthest from the heatsource. Thus the greater heat that reaches the adhesive closest to theheat source has even less tendency to hurt that adhesive while the heatreaching the farthest adhesive is adequate to set this adhesive.

Preferably, as already set forth hereinabove, the liners are made fromhighly calendered pure kraft paper which are of high density but whichare of different weights for the outermost two layers may be made ofvery heavy weight while the two liners in between may be made of lighterweight paper. This has the great advantage that the one thicker layerclosest to the heat receives its heat directly, the adhesive on theinside of the liner farthest from the heat receives heat without itpassing through this liner, and the two liners in between are both ofthe lighter and therefore thinner paper that does not resist the passageof heat to so great a degree.

A further feature of the invention is to use an adhesive of a type thatmay be heated to high temperatures before it is applied to the tips ofthe corrugations of the corrugated medium in the case of the combiningof all of the parts to produce the triple wall construction. Suchadhesive may be a formula consisting largely of silicate of soda,starch, clay, water and other additive. The starch acts as a sort ofdesiccating or dehydrating agent, in that in conversion orgelatinization wit-h heat it absorbs the water available from thesilicate of soda. The silicate of soda of course sets when a certainpercentage of water (e.g. between 13.5% and 15%) is removed from it.

As a matter of fact all of the adhesive is located between the tips andthe flat liners and none of the adhesive has the characteristic ofadhesive that has been first hardened and then rewet such as would occurif previously made single wall or double wall components were later oncombined by manual methods using new glue, the water of whichnecessarily resoftened the previously hardened glue.

The present invention permits the rapid and effective production oftriple wall corrugated paper board of great strength even when the outerliners or fiat sheets are made of so called water-proof ormoisture-proof pure kraft paper, and even though the corrugated mediumis made of heavier than usual paper for the purpose of even furtherincreasing the strength of the final product as will be ascertainedhereinafter.

Another object of the present invention is to provide a scoring devicefor multiple wall corrugated fibre board. Scoring devices are knownwhich comprise at least one pair of registering rotatable score wheelsbetween which the finished board is pulled and constituting the one amale die having in cross-section a projecting forming part and the othera female die having in cross-section a corresponding depression. Thescoring device according to the invention is remarkable notably in thatsaid male die overlies said female die so as to engage from above thetop surface of said board, said male die projecting part forming araised arcuate portion around its periphery and about three-quarters ofan inch wide and about three-sixteenths of an inch high whereas saiddepression around the periphery of said female die which issubstantially exact mate of the male has dimensions corresponding tothose of the male.

This invention also relates to the multiple wall corrugated fibre boardproduct manufactured according to the method broadly set forthhereinabove and comprising a plurality of layers of corrugated mediuminterspersed between fiat liners which are of heavier weight on the twooutermost layers than those forming the inner layers which thus arerelatively thinner. This product is remarkable notably in that saidliners are all of equally very high density and preferably made ofhighly calendered pure kraft paper and are joined together with saidcorrugations on one side of the corrugated medium by at least one typeof adhesive and on the other side by at least another type of adhesive,the adhesive being confined to the interconnecting parts and being firmand free from over-heating effects throughout the entire product.

According to another very important feature of the present invention,said multiple wall fibre board product comprises corrugated medium ofrelatively very heavy weight combined with liners at least some of whichare of possibly relatively reduced weight and caliper.

In effect, this invention advocates the use of heavier corrugatingmediums for the purpose of increasing not only the column compressionload which the finished fibre board may withstand but also itsresistance to puncture by sharp objects during transit. It hasfrequently and emphatically been stated in prior art and present tradepractice that the strength of combined corrugated fibre board except asconcerns flat crush is entirely dependent of the strength of the linersor flat sheets and that the sole purpose of the corrugating medium isthat of spacing the liners sufiicient-ly from the neutral axis of theboard for the development of maximum strength by the fibre board. Theweight and thickness of the corrugating medium have thus far beenconsidered unimportant in their contribution to strength.

It was found, to the contrary, that the weight and thickness of thecorrugating medium contribute markedly to an increase in strengthespecially in resistance to puncture. The increase is so marked thatincreases in strength due to small increases in the weight and caliperof the medium are more than sufficient to overcome potential losses dueto a large decrease in the weight and caliper of the liner sheets.Typical test results as concerns column compression and puncture areshown in the following Table I for different constructions of triplewall corrugated fibre board. It is evident from the examination of thistable that an increase in the weight of the liners results in anincrease in the strength of the board, a result which is in accord withpast experience. Examination of sample No. 1 fibre board shows that anincrease in the weight and caliper of the liner sheets of 21% and 10.5%respectively over those of sample No. 2 produces a 7% increase in thepuncture resistance of the board and a 5.75% increase in the compressionresistance of the board. The total paper weight change is 14.5%.

While previous experience indicates that the increase of weight andcaliper of the medium contributes little to column compression strengthand nothing to puncture resistance, examination of samples 2 and 3 showsthat increasing the weight and caliper of only the medium in sample No.3 by 27% and 20% respectively over those of sample No. 2 produces anincrease of 17.5% in puncture resistance and 10% in compressionresistance. The total paper weight change is 8.2%. Furthermore,comparison of samples 1 and 3 shows that despite the decrease of 17.3%and 9.5% in liner weight and caliper respectively of sample No. 2, adecrease which is considered to be large, an actual increase of 3% inpuncture resistance and 4% in compression resistance was obtained. It isimportant to note at this point that the increase in corrugating mediumweight and caliper between these samples of 27% and 20% respectively,not only offset the loss in strength due to the decrease in liner weightand caliper, but in actual fact raised the strength of the board. Theoverall weight change of the board is a decrease of less than 6 Sample 4is included in Table I to indicate that intermediate weight and caliperof liners will produce intermediate strength results. This would beexpected from the foregoing paragraphs.

In normal plant production, where board is made using adhesives exactlylike the adhesives used in making the fibre board described in Table Iand where similar grades of paper are used, but obviously not from theexact same roll-s, we have found that grades of board exactly like thoseshown as sample 2 of Table I may have a puncture value which ranges froma low of 1000' to a- TABLE I.IROPERTIES AND TEST RESULTS OF TYPICALTRIPLE WALL CORRUGATED FIBRE BOARDS (C-A-A TYPE FLUTE CONFIGURATION)Fibre Board Total Liner Properties Total Medium Properties Total FibreBoard construction Properties Sample Puncture, Compression,

No. in.-oz./in. s./in.

Liner Weight, lbs./ Caliper, Weight, lbs./ Caliper, of tear Weight,lbs./ Caliper, Arrange- Mediums 1,000 sq.tt. in. 1,000 sq.ft. in. 1,000sq.ft. in.

ment

90646et90 26 331. 6 0. 084 2 119. 6 0.030 1,155 (1, 187) 165 451. 20.114 904242-90 26 274. 2 0. 076 119. 6 0.030 1,080 156 393. 8 0. 10690-42-42 90 33 274. 2 0. 076 152. O 0. 036 1, 189 172 426. 2 0. 11290-64-42-90 26 302. 9 0. 080 119. 6 0. 030 1, 112 153 422. O. 110

1 Weights and calipers of individual liners and mediums used in theabove boards:

lineal length of medium 2 Take-up factor of 1.5 used for A-llute and1.43 for C llute= The increase in puncture resistance wrought by theinclusion of heavier and thicker corrugating mediums in triple wallcorrugated fibre board is all the more remarkable when examined in thelight of past practice in meeting minimum standards for corrugated fibreboards. The minimum standards for corrugated fibre boards is set forthfor example in the U.S. Uniform Freight Classification under Rule 41.This rule specifies that each grade of board must meet a minimum burstor puncture strength. In the case of some boards, the burst strengthmeasured by the Mullen or Cady test is beyond the capacity of thetesting machine used to test it. Under these circumstances, a puncturetest (Beach test) is used. While the two tests are not the same, theresults are comparable since the unit of puncture, inch-ounces per inchof tear, were chosen so that it would correspond to a burst reading.

In an attempt to meet the specifications under Rule 4 1, it is commonpractice to determine the burst strengths of the liners only and placein the finished board liners whose total burst strength is equivalent tothe burst strength desired in the finished board. The corrugating mediumis ignored completely. For example, if a double wall board of 600- testwere desired, the liners would be chosen such that the sum of theirindividual burst values would be 600. No account is taken of the medium.

This practice when used with triple wall board, would produce errors ofconsiderable magnitude. In the case of sample 2 in Table I a burst orpuncture strength of only 570 could be predicted. Certainly, this methodcan never predict that with a net decrease of 21% in liner weight couldany increase in burst or puncture be obtained.

The inclusion of heavier mediums in triple Wall corrugated fibre boardwhile at the same time reducing the weight of the flat sheets or linershas a second important advantage in the overall manufacture of theboard. As has been previously indicated, the transfer of heat to theuppermost adhesive line during the combining operations of FIGURE 2 isboth difficult and critical. Any

arrangement of liners, mediums or air space between them lineal lengthof single face liner 'where Q is the amount of heat transferred, At isthe temperature difference across the sample and R- is the resistance tothe flow of heat. The resistance R is in turn determined by means of therelationship where k is the thermal conductivity of the material, L isthe thickness of the material, and A is the area exposed to the heatsource. In any multi-layer material, the total resistance to heat flowis the sum of the individual resistances. Therefore the heat transferredthrough a multi-layer material such as corrugated fibre board is givenby the equation AAt & E L3 /c lc k (4) In reducing the thickness of theliners, the quantity L in Equation 2 is lowered, leading in turn, to areduction in the resistance R. In accordance with Equation 1 the amountof heat transferred through the board is greater. It must be rememberedthat increasing the thickness of the corrugating medium has the oppositeeffect. However, the total change due to reducing the liner thicknessand increasing the medium thickness is a net reduction in overall paperboard thickness through which the heat must travel.

The use of thicker mediums also causes the gas or vapor layer betweenthe liner and the medium to be reduced. This occurs since the singlefacer produces a flute of definite height which will be only slightlyaffected by the corrugating medium. If the cross sectional area, andthus the volume between the inner faces of the liners thus remainsconstant, it is obvious that the thicker corrugating mediums will occupya greater amount of volume thus reducing the vapor volume andconsequently its effective thickness. This reduction in thickness of theair layer again results in greater conductive heat transfer. The totalincrease in the amount of heat transfer by conduction is between 3 and4%.

The steam and air stream rising through the board is the second majormeans by which heat is transferred through the fibre board. The heatedair portion of the stream transfers heat to the adhesive and the boa-rdcomponents which are furthest from thehea-t source through loss ofsensible heat. The steam transfers heat not only through loss ofsensible heat but also through repeated condensations and evaporations.However, the effect of the latter is small. The percentage of air in themixed stream increases as the stream moves up through the board with aresulting decrease in the partial pressure of water vapor. Thus thesteam is held mainly in the vapor form and transfers heat through lossof sensible heat or superheat.

Since it is essentially a vapor stream that is responsible for heattransfer, the amount of heat transferred is a function of the amount ofvapor which is capable of passing up through the interstices of thecomponents. The passage of a fluid through any opening is given by aformula of the Poiseuille type dF 32/LV dL gcD V (5) It can be seen,that all other things being equal, the volume of fluid V capable ofpassing through an opening of diameter D is inversely proportional tothe length L of the opening.

In the present invention, the use of thicker medium while at the sametime using thinner liners results in a net decrease in thickness ofpaper contained in the final combined board (see Table 1). Thus there isa net decrease in the length of the openings resulting in a greater flowof vapor and a greater amount of heat transfer.

One must also take into account the factor D, the diameter of theopening, in Equation 5 which shows that the amount of vapor is directlyproportioned to the square of the opening. In the present inventiondense liners are used having small interstices. By comparison, thecorrugating medium is porous having larger interstices. Thus even forthe same thickness of total board, the flow of vapor would be greatestwhere the medium thickness is a larger percentage of the totalthickness.

Examination of Table I reveals that the medium constitutes 26% of .thetotal paper thickness in sample 1 as compared to 32% in sample 3. Thetotal effect, therefore, of caliper and porosity gives an increase inheat transfer from 5 to 6 percent, or a grand total including conductionof 8 to 10 percent.

A further advantage of the present invention relates to the cost of thefinished triple wall corrugated fibre board. Comparison of samples 1 and3 of Table I shows that board of greater strength can be obtained byusing thicker corrugating mediums and thinner liners despite the factthat there is a net reduction in the total weight of paper board in theproduct. Since paperboard is purchased on a weight basis, there isobviously a net saving involved in using a lower weight of paper. Thissaving is amplified when it is remembered that the cost of corrugatingmediums is lower than the cost of liner. Thus, in the present inventionlow cost medium is substituted for high cost .liner with an overallreduction in total weight resulting in significant savings.

In summary it has been ascertained that significant increase in strengthand heat transfer and'significant savings can be obtained where themedium weight and caliper are 33 lbs./1000 ft. and0.012" respectivelyand where the medium weight and caliper ranges from 30 10 lbs/1000 ft.and 0.011 inch respectively to the heaviest and thickest medium which itis practical to corrugate. This discovery is directly contradictory tothe prior literature and art relating to normal corrugated fibre boardand to heavier corrugated fibre board structures.

Other objects, features and advantages of the present I invention willbecome apparent as the following description proceeds with reference tothe accompanying diagrammatic drawings given by way of example only forillustrating a form of embodiment of the invention and in which:

FIG. 1 is a partial elevational side view of one single facer section ofa corrugated fibre board machine showing the step wherein the corrugatedmedium is applied to one liner;

FIG. 2 is an enlarged partial side View of the double backer section ofsaid machine showing the combining step wherein all three single facecomponents and the fourth liner are put together;

FIG. 3 is an enlarged vertical section parallel to the direction oftravel of the paper showing the effective adhesive bond obtained betweenall of the tips of the corrugation and the adjacent liner;

FIG. 4 is a perspective partial view of a scored board showing thepossibility of creasing or scoring the new product so it may be foldedas required to make a rectangular box for example;

FIG. 5 is a fragmentarycross-section of the score dies;

FIGS. 6, 7 and 8 are graphs based upon test data included in Table Igiven hereinabove and wherein puncture and column compression strengthsare plotted against total board weight, total liner weight and totalliner caliper respectively.

Referring now to the embodiment in FIG. 1, the corrugating mediumdenoted by the reference numeral 1, is first formed in the nip betweencorrugating rolls 2 and 3 after first conditioning the medium withmoisture as by steaming and with both corrugating rolls being properlyheated. While on roll 3, the medium 1 has lines of adhesive 4, appliedto each tip of each corrugation by means of adhesive applicator roll 5.The usual starch or silicate adhesive may be used provided it iscompounded to set at higher temperatures. In the case of sodiumsilicate, a normal 38 B. solution having a silica (SiO to soda (Na O)ratio in the range of 3.2 to 3.33 may be used directly. In the case ofstarch a mix containing 20% solids and having 33 pounds of caustic in a666 gallon batch will be satisfactory. In addition, the previouslydescribed type of silicate adhesive containing starch protein and otheringredients besides water may be used.

In all cases enough water is used to provide a fluid consistency (with aviscosity of 50 to 120 Saybolt seconds for example for silicate typeglue). The exact corrugating material used may be any of thosecustomarily used in making the older kinds of corrugated paper board.The material that is considered to be best is medium weighing 33 to 36pounds per 1000 square feet as stated hereinabove.

The liner 6 after being suitably heated is fed over a heated roll 7which presses the liner 6 against the tips of the corrugations of medium1, the heat causing the adhesive to set enough to hold the twocomponents to gether thereafter.

This liner may be for example very dense highly calendered pure kraftpaper. It may weigh pounds per 1000 square feet but due to its densityit is not very thick. It is directly in contact with the heated roll 7.The corrugated medium 1. is of course hot from the corrugating step andtherefore the adhesive may be set easily during this phase of themanufacture.

On the other hand the liner 6 may be of relatively light paper whenintended for the mid portions of the final product. In these instancesalthough still a more dense heavily calendered pure kraft paper, theliner may weigh only 42 pounds per 1000 square feet.

The liner material of the desired kind is only about .023" to .030"thick in the case of the 90 pound material and is only .013" to .016thick in the case of the 42 pound material.

In FIG. 2 the three layers of the materialshown being made in FIG. 1,are placed together with a fourth liner, this beneath the corrugationsthat would otherwise be exposed. Before being thus combined the tip ofeach exposed corrugation has the second adhesive 9 applied to it againin the form of a line running along the tip of the corrugation. In thiscase the adhesive is of the lower temperature setting formula.

As shown by FIG. 2 all corrugations were made during the steps shown byFIG. 1 with the top two relatively high or deep corrugations while thebottommost corrugations were made shallower or less high. The liner 6and the liner of the top component are made of the heavier but densepaper while the other two liners were made of the lighter linermaterial. If desired, the adhesive 9 applied to the exposed corrugationsof the top layer has a formulation permitting the lowest temperaturesetting of all.

During the step of FIG. 2 all of the liners or fiat sheets are held flatand straight and free from curvature insofar as is possible. The layersare all pressed together because the liner 10 is resting on a heatedplate 8 while a belt 11 at the uppermost liner 12 presses all of thelayers together against the hot plate 8. Continuous production ispossible by causing the various layers to move while under theconditions noted but in such an event care must be taken as to permitthe layers to have no movement relative to each other.

It is considered best to heat the plate 8 to temperatures ranging about300 F. to some thirty or more degrees higher. The exposure time of thelayers being put together at such heat may vary from a minimum wherethere is danger of destroying the integrity or strength of the layer upto maximum, such as might be desired for high speed manufacture, that isjust sufficient to set the adhesive 9 enough to hold the product firmlytogether. Moisture from the adhesive and from other causes should ofcourse be driven off to a considerable degree.

As previously explained the density of the liner 1.0 promotes heatconduction through this layer. The small size of the first set ofcorrugations permits this heat to get quickly to the liner or fiat sheetto which the first set of corrugations were previously attached. Theonly barriers then in the way of heat transfer are the two substantiallythinner next upwardly flat liners and the air space produced by thecorrugating medium between them. Radiation plus the thermal bathprovided by rising steam gets the heat to the most diflicult to setlocations, namely the lines of adhesive located on the bottoms of thecorrugations of the upper most layer of previously put togethercorrugated medium and heavier liner sheet.

During this necessarily high temperature working, the previously appliedlines of adhesive 4 are not damaged because they consist of the adhesivehaving the higher temperature setting characteristic and thereforerelatively unaffected by the temperatures used during this overallcombining step. Specific usable compositions of adhesive are as follows:

For the first step, 38 B. silicate may be used where a silicate formulais desired. Where a starch formula is desired an adhesive containing 33pounds of caustic in a 666 gallon batch may be used giving a causticcontent of about 2.7%.

For the second step, about 12% clay is added to the silicate where asilicate formula is desired. The caustic content is raised to 40 poundsin a 666 gallon batch giving a caustic content of about 3.3% where astarch formula is desired. For the uppermost last applied adhesive aformula containing 70% silicate, 6% starch, 18% clay and 6% borax isused where a silicate formula is required. Where a starch formula isdesired, the formula given under the second step may be modified tocontain about 20% of a polyvinyl acetate emulsion. All percentagesspecified are on a dry adhesive weight basis.

In all cases the adhesive 9 must be set firmly enough to permit therelatively thick product to be handled. As to thickness, the upper twolayers of corrugated medium may be of the so-called A-type defined by aflute depth in the neighborhood of 9& of an inch with about thirty-sixcorrugations per lineal foot, wherea the lowermost corrugated mediumhaving reference to FIG. 2, may be made with so-called C-typecorrugations having a depth or height of about of an inch with about 42corrugations per lineal foot. The whole finished product may have athickness of about 7 inch. In FIG. 3 the general contour of the finishedbond of adhe ive 9 is shown as having the usually desired but not alwaysattained restriction close to the tip of the corrugation,

which applies to all instances, and as having lateral edges which areconcave because they form the meniscus of the liquid adhesive prior tosetting. This type of bond is recognized as being highly desirable andcan be attained in the case of thin corrugated paper products. It is notordinarily obtainable throughout the length of the adhesive line in thecase of triple wall material such as has been described.

Overheating causes the embrittlement of the adhesive so that theadhesive cracks or breaks when the board is handled resulting in theseparation of the previously combined layers. Relative slippage betweenlayers before the adhesive is properly set causes the corrugated tips towipe the adhesive in a wide band along the width of the board leaving aninadequate amount of adhesive in the correct position between thecorrugated tip and the liner for a proper bond between the components.This wiping also causes the board to lose its proper configuration. Thepresent invention provides for the most desirable bond throughout thedesired product.

With all of the adhesive set satisfactorily there arises the problem ofcreasing or scoring this very thick product without breaking or crackingany of the layers such as would destroy strength at the bend requiredfor right angular parts. In the case of the present invention this canbe done immediately following the step shown in FIG. 2 preferably beforethe combined board has been cut and while some moisture still remains inthe fibre board. All of this moisture need not be driven out during theFIG. 2 step because of the effectiveness of the new features previouslydescribed.

Such creasing or scoring is shown by FIG. 4. The corrugations of boa-rd13 are of course crushed but throughout a relatively wide zone,indicated at d and the various liners move towards each other. This zoned should be much wider than that ordinarily used for thinner corrugatedmaterials.

The particular score line that is considered most effective is the onethat would be made by the set of score wheels shown in FIG. 5. The malescore wheel 14 has a raised portion 15 around its periphery at the pointwhere the board is to be scored. The dimension a, the width of theraised portion, is about three-quarters of an inch while dimension b,which is the height of the raised portion, is about three-sixteenths ofan inch. The female score wheel 16 is an exact mate of the male and hasaround its periphery a depression 17 whose dimensions correspond tothose of the male.

In operation, the male score is pressed into the board perpendicular tothe axis of the corrugations. The corrugation are crushed in a bandalong the length of the board. The upper liner conforms exactly to thecontour of the raised portion of the male score wheel. The bottom lineris not pushed completely into the depression of the female score wheelbecause of the crushing of the corrugations. However, in the finishedscore the liner in contact with the female score wheel does extend belowthe surface of the board.

This type of score offers the advantage that it stresses the board inthe direction in which this portion must eventually be stressed after acarton is produced from the board. The score herein described is a flapscore which is to say that it produces a line of bend in the board whichseparates the flaps used in forming the top and bottom of the box fromthe sides of the box.

When a carton is made from the fibre board described, the flaps are bentinwards towards the center of the carton. Under these circumstances, theliner which had previously been in contact with the male score isgreatly depressed while the liner which had previously been in contactwith the female score, is greatly elongated. The score described tendsto stress the liners in just this manner so that the bend is made easilyand the liners will suffer no damage during the bending operation.

The scoring or creasing need not be followed by bending or folding ofthe product. The product in convenient lengths is preferably stacked andgiven time for What might be called a cure. During this time anyremaining moisture evaporates and the fibre board components acquire amoisture content that is stabilized with respect to the humidity of thesurrounding atmosphere. In some cases further setting of the adhesivemay occur during this period.

The foregoing produces a new product in the form of three layers ofcorrugated medium, two of which have deep corrugations, and one ofwhich, on the outside of the central one, has less deep corrugations.These three components are interleaved between the four layers or flatsheets of which the outermost ones of the latter are of the relativelyheavy but very dense pure kraft paper while the inner two are of equallydense but somewhat thinner pure kraft paper.

The adhesive bond is in all cases of the type as shown in FIG. 3. Theuse of the two types of adhesive is made evident by this bond and itscharacteristics because otherwise the lowermost bond points would nothave the desired characteristics but would be brittle, out of shape andweak.

Furthermore, by crushing the score or crease lines as shown by FIG. 4 sothat the bottommost layer will form the outside of any parts creased torectangular shape, breaking of the liners is prevented during suchcreasing, particularly the bottommost or outermost liner. The relativelyshall-ow lowermost or outermost layer of corrugated medium also helpsprevent breaking of the outer liner since there is less paper in theshallow corrugation which will bear on the outer liner. Also, externalcrushing such as may be occasioned by placing concentrated loads on thesurface of the board is to a large extent eliminated because theshallower corrugations provide a greater rigidity in the direction ofsuch pressure. Referring now to the graphs of FIGS. 5-7 based upon thedata included in Table 1:

Graph of FIG. 6 shows the puncture and compression properties of theboard plotted against total board weight. The curves connect test pointsS S 8., representing samples l, 2 and 4 respectively which include thelight weight medium with varying thicknesses of intermediate liners.Thus, the variable for the curves is the liner weight. These curvesdemonstrate and support the prior art concept that increases in theliner weight increase the puncture and compression properties of theboard. The points S and 8;, on this graph represent the heavy mediumtriple wall board and demonstrate the marked increase in puncture andcompression properties. Curves are not shown for the heavy medium triplewall since the data only includes sample No. 3.

It is presumed that if additional data was available for the heavymedium triple wall, curves could be drawn through the points S whichwould lie above the curves for the light weight medium. In probabilitycurves for the heavy medium triple wall would extend to the left of thegraph towards a common origin with the curves of the light weightmedium. Thus, the slope of the heavy medium curves would be appreciablygreater than that of the light weight medium curves. The increasedslope, which represents the ratio of the properties to the total boardweight, is a measurement of the efiiciency of the board and thus theheavy medium triple wall is shown to have greater efiiciency as well asabsolute values for the puncture and compression properties.

The graphs of FIGS. 7 and 8 show curves for the light weight mediumagainst total liner weight and total liner caliper, respectively. Asdiscussed with respect to the curves in FIG. 6, the graphs of FIGS. 7and 8 also demonstrate the prior art concept that the properties of theboard are dependent upon liner weight and liner caliper. Again as inFIG. 6, the points S 8;, representing the heavier medium triple wallpoint out the marked improvement achieved by this arrangement.

It is felt that the graphs demonstrate why the prior art practice hasbeen to vary liner weight and caliper alone in order to obtain increasedpuncture and compression properties but not to vary the medium weightand caliper.

The available data is limited to that of Table I and therefore it isimpossible at the present time to provide any further graphicalpresentation of the heavy medium triple wall against the light weightmedium triple wall.

The scope of the present invention should not be construed to be limitedto the forms of embodiment herein described and shown which have beengiven by way of example only.

What is clamed is:

1. A method of making triple wall corrugated paper board having fourliners and three corrugated paper mediums individually interposedbetween two liners in each instance, the corrugations of said mediumsbeing parallel to each other throughout said board, said methodcomprising the steps of bonding each of the corrugated mediums at oneside thereof to a different one of the liners with a first adhesivehaving a first predetermined setting temperature to form a single facecorrugated paper board sheet, heating each of said single face sheets toraise the temperature of said first adhesive at least to said firstsetting temperature to initially set said first adhesive, applying asecond adhesive to the ridges at the opposite side of said single facesheets, said second adhesive having a second setting temperature whichis lower than said first setting temperature of said first adhesive,combining at least three of said single face sheets with mediums bondedthereto in juxtaposition with an additional liner, the medium of two ofsaid single face sheets during said combining being placed contiguouswith the liner of the single face sheet adjacent thereto and the mediumof the other one of said single face sheets during said combining beingplaced contiguous to said additional liner, and additionally heating thecombined single face sheets and the additional liner to raise thetemperature of said second adhesive to at least said second settingtemperature to set said second adhesive and to set further said firstadhesive, the lower setting temperature of said second adhesive enablingsaid second adhesive to be set by said additional heating at atemperature which safeguards said first adhesive from overheating.

2. A method in accordance with claim 1 in which the step of bonding acorrugated medium to a liner with said first adhesive having a firstpredetermined setting temper ature to form a single face corrugatedpaper board sheet further comprises using for said first adhesive anadhesive which may be heated to high temperatures before it is appliedto the tips of the flutes of the corrugated medium, said first adhesiveincluding sodium silicate, starch, clay, water, and additionaladditives.

3. A method in accordance with claim 1 in which the step of bonding acorrugated medium to a liner with said first adhesive having a firstpredetermined setting temper- .ature to form a single face corrugatedpaper board sheet further comp-rises the using for said first adhesiveone of the high temperature setting adhesive of a normal 38 B. gravitysodium silicate solution having a silica to soda ratio in the range of3.2 to 3.33 and the high temperature setting adhesive of a starchmixture containing 20% solids and having 33 pounds of caustic in a 666gallon batch, said starch mixture having a caustic content of about2.7%.

4. Triple Wall corrugated paper board which is fiat and adapted forscoring and bending to form a shipping container comprising four paperliners, the outermost liners weighing about 90 pounds per 1000 squarefeet and being from about .023 to about .030 of an inch thick, twointermediate liners weighing about 42 pounds per 1000 square feet andbeing from about .013 to about .016 of an inch thick, three corrugatedpaper mediums, the mediums being interposed between the liners in eachinstance with the corrugations of the medium being parallel to eachother per 1000 square feet and from about .011 to about .018

of an inch, respectively, first and second adhesive applied to theridges of the mediums corrugations for intimately and rigidly bondingthe mediums and liners together, said first adhesive bonding each of thecorrugated mediums at one side thereof to a different one of the liners,to form a single face corrugated paper board sheet, said first adhesivehaving a first predetermined setting temperature and being one of asodium silicate mix added with about 12% clay and a starch mixturecontaining 40 pounds in a 666 gallon batch and giving a caustic contentof about 3.3%, said second adhesive being applied to the ridges at theopposite side of the medium of each of said single face sheets andhaving a second setting temperature which is lower than said firstsetting temperature of said first adhesive, said second adhesive beingof a sodium silicate formula containing about 70% sodium silicate, 6%starch, 18% clay, and 6% borax on a dry weight basis and a starchformula modified to contain about 20% of a polyvinyl acetate emulsion,the lower setting temperature of said second adhesive enabling saidsecond adhesive to be set by said additional heating at a temperaturewhich safeguards said first adhesive from overheating.

5. A method for making triple wall corrugated paper board having fourliners and three corrugated paper mediums individually interposedbetween two liners in each instance, the corrugations of said mediumsbeing parallel to each other throughout said board, said methodcomprising the steps of bonding each of the corrugated mediums at oneside thereof to a different one of the liners with a first adhesivehaving a first predetermined setting temperature to form a single facecorrugated paper board sheet, said first adhesive being one of a sodiumsilicate mix added with about 12% clay and a starch mixture containing40 pounds in a 666 gallon batch and giving a caustic content of about3.3%, heating each of said single face sheets to raise the temperatureof said first adhesive at least to said first setting temperature toinitially set said first adhesive, applying a second adhesive to theridges at the opposite side of the medium of each of said single facesheets, said second adhesive having a second setting temperature whichis lower than said first setting temperature of said first adhesive,said second adhesive being one of a sodium silicate formula containingabout sodium silicate, 6% starch, 18% clay, and 6% borax on a dry weightbasis and a starch formula modified to contain about 20% of a polyvinylacetate emulsion, combining at least three of said single face sheets injuxtaposition with an additional liner, the medium of two of said singleface sheets during said combining being placed contiguous with the linerof the single face sheet adjacent thereto and the medium of the otherone of said single face sheets during said combining being placedcontiguous to said additional liner, and additionally heating thecombined single face sheets and the additional liner to raise thetemperature of said second adhesive to at least said second settingtemperature to set said second adhesive and to set further said firstadhesive, the lower setting temperature of said second adhesive enablingsaid second adhesive to be set by said additional heating at atemperature which safeguards said first adhesive from overheating.

References Cited by the Examiner UNITED STATES PATENTS 2,160,221 5/1939Masters et a1 161-137 2,434,466 1/1948 Marc 161137 2,759,523 8/1956Goldstein et al 156'268 2,985,553 5/1961 Anderson 1611'37 3,033,7085/1962 McKee 1l7l19.8 3,096,224 7/1963 Goldstein et al 161--137 EARL M.BERGERT, Primary Examiner.

R. I. SMITH, M. L. KATZ, Assistant Examiners.

4. TRIPLE WALL CORRUGATED PAPER BOARD WHICH IS FLAT AND ADAPTED FORSCORING AND BENDING TO FORM A SHIPPING CONTAINER COMPRISING FOUR PAPERLINERS, THE OUTERMOST LINERS WEIGHING ABOUT 90 POUNDS PER 100 SQUAREFEET AND BEING FROM ABOUT .023 TO ABOUT .030 OF AN INCH THICK, TWOINTERMEDIATE LINERS WEIGHING ABOUT 42 POUNDS PER 100 SQUARE FEET ANDBEING FROM ABOUT .013 TO ABOUT .016 OF AN INCH THICK, THREE CORRUGATEDPAPER MEDIUMS, THE MEDIUMS BEING INTERPOSED BETWEEN THE LINERS IN EACHINSTANCE WITH HE CORRUGATIONS OF THE MEDIUM BEING PARALLEL TO EACH OTHERTHROUGHOUT SAID BOARD, TWO OF SAID MEDIUMS BEING MADE WITH DEEPCORRUGATIONS OF THE A-TYPE HAVING A FLUTE DEPTH OF ABOUT 3/16 OF AN INCHWITH ABOUT 36 FLUTES PER LINEAL FOOT, AND A THIRD OF SAID MEDIUMS ON THEOUTSIDE OF THE CENTRAL ONE BEING MADE WITH LESS DEEP CORRUGATIONS OF THEC-TYPE HAVING A FLUTE DEPTH OF ABOUT 5/32 OF AN INCH WITH ABOUT 42FLUTES PER LINEAL FOOT, THE WEIGHT AND CALIPER OF THE MEDIUMS BEING IN ARANGE FROM 30 POUNDS TO ABOUT 52 POUNDS PER 1000 SQUARE FEET AND FROMABOUT .011 TO ABOUT .018 OF AN INCH, RESPECTIVELY, FIRST AND SECONDADHESIVES APPLIED TO THE RIDGES OF THE MEDIUMS'' CORRUGATIONS FORINTIMATELY AND RIGIDLY BONDING THE MEDIUMS AND LINERS TOGETHER, SAIDFIRST ADHESIVE BONDING EACH OF THE CORRUGATED MEDIUMS AT ONE SIDETHEREOF TO A DIFFERENT ONE OF THE LINERS, TO FORM A SINGLE FACECORRUGATED PAPER BOARD SHEET, SAID FIRST ADHESIVE HAVING A FIRSTPREDETERMINED SETTING TEMPERATURE AND BEING ONE OF A SODIUM SILICATE MIXADDED WITH ABOUT 12% CLAY AND A STARCH MIXTURE CONTAINING 40 POUNDS IN A666 GALLON BATCH AND GIVING A CAUSTIC CONTENT OF ABOUT 3.3%, SAID SECONDADHESIVE BEING APPLIED TO THE RIDGES AT THE OPPOSITE SIDE OF THE MEDIUMOF EACH OF SAID SINGLE FACE SHEETS AND HAVING A SECOND SETTINGTEMPERATURE WHICH IS LOWER THAN SAID FIRST SETTING TEMPERATURE OF SAIDFIRST ADHESIVE, SAID SECOND ADHESIVE BEING OF A SODIUM SILICATE FORMULACONTAINING ABOUT 70% SODIUUM SILICATE, 6% STARCH, 18% CLAY, AND 6% BORAXON A DRY WEIGHT BASIS AND A STARCH FORMULA MODIFIED TO CONTAIN ABOUT 20%OF A POLYVINYL ACETATE EMUULSION, THE LOWER SETTING TEMPERATURE OF SAIDSECOND ADHESIVE ENABLING SAID SECOND ADHESIVE TO BE SET BY SAIDADDITIONAL HEATING AT A TEMPERATURE WHICH SAFEGUARDS SAID FIRST ADHESIVEFROM OVERHEATING.